Efficient iron-based ammonia decomposition catalyst based on MCM-41 carrier as well as preparation method and application of efficient iron-based ammonia decomposition catalyst

Abstract

The invention belongs to the technical field of catalysts, particularly relates to an ammonia decomposition hydrogen production catalyst and a preparation method and application thereof, and aims at the technical bottlenecks that an existing iron-based catalyst is low in activity, poor in stability and the like in an ammonia decomposition reaction, a mesoporous material MCM-41 is innovatively adopted as a carrier, and iron trioxide is loaded for ammonia decomposition hydrogen production, so that the catalyst is prepared. The problems that an iron-based catalyst is low in catalytic activity and easy to sinter in the ammonia decomposition process are effectively solved, and an efficient and reliable catalyst solution is provided for industrial application of an ammonia decomposition hydrogen production technology.

Description

Technical Field

[0001] This invention relates to the field of catalysts, specifically to an ammonia decomposition hydrogen production catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia decomposition technology, as an important chemical process, is widely used in hydrogen production, gas purification, and energy conversion. Its core lies in the development and application of highly efficient catalysts, among which iron-based catalysts have attracted international attention due to their low cost and widespread industrial application in ammonia synthesis.

[0003] MCM-41, as an ordered mesoporous material, has attracted much attention in the field of catalysis since its introduction. Its structural features include a highly ordered hexagonal mesoporous arrangement and a high specific surface area (>1000 m²). 2 With its adjustable pore size (g / g), MCM-41 provides an ideal platform for catalytic reactions. It can also serve as a highly efficient catalyst support, improving dispersion and stability.

[0004] While the industrialization of iron-based catalysts in ammonia decomposition technology is progressing, optimizing the catalyst's composition, structure, and pretreatment conditions to further enhance its catalytic activity and stability remains a key research challenge. Currently, most iron-based catalysts exhibit low activity and poor stability. Therefore, this invention aims to provide a novel iron-based catalyst, its preparation method, and its applications, with the goal of achieving higher catalytic activity and stability in ammonia decomposition reactions. Summary of the Invention

[0005] One of the technical problems to be solved by this invention is to provide a catalyst for hydrogen production from ammonia decomposition that does not use precious metals, thereby solving the problems of low activity and poor stability of existing iron catalysts.

[0006] The second technical problem to be solved by this invention is to provide a low-cost in-situ pretreatment method corresponding to the first problem. The catalyst synthesized by this method has higher ammonia decomposition activity and reduces the industrialization cost of ammonia decomposition hydrogen production technology.

[0007] To solve one of the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preparing a catalyst for ammonia decomposition to hydrogen production involves using MCM-41 as a support to support ferric oxide as a supported iron-based catalyst for ammonia decomposition to hydrogen production technology.

[0008] The specific steps for preparing the supported iron-based catalyst are as follows: Preparation of ferric oxide: First, 1.6 g of iron source and 6.3 g of sodium acetate were weighed and added to 60 mL of ethanol, and the solution was stirred at room temperature for 30 min. Next, 1 mL of deionized water was added to the prepared solution, and the mixture was stirred for 30 min. Then, the solution was transferred to a 100 mL hydrothermal reactor and kept at 180 °C for 24 h. Finally, the mixture was filtered, washed three times each with deionized water and ethanol, and placed in an 80 °C oven until completely dry. After drying, the sample was placed in a muffle furnace and calcined at a certain temperature with a heating rate of 5 °C / min.

[0009] Preparation of MCM-41 molecular sieve: First, weigh 2.0 g of cetyltrimethylammonium bromide and dissolve 70 mL of concentrated ammonia in 420 mL of water. After the solution is clear, add 10 mL of tetraethyl orthosilicate and stir for 2 h. Filter the solution and wash it three times each with deionized water and ethanol. Place it in an 80 ℃ oven until completely dry. After drying, place the sample in a muffle furnace and calcine it at 550 ℃ for 5 h at a heating rate of 5 ℃ / min.

[0010] Preparation of supported catalyst: A certain amount of ferric oxide was weighed and dispersed in a crucible containing an appropriate amount of deionized water. After the dispersion was uniform, 0.4 g of support was added and stirred for 30 min. Then, the crucible containing the mixed suspension was placed in an oven at 80 ℃ and dried for 12 h. Finally, it was calcined in a muffle furnace at a heating rate of 5 ℃ / min to 500 ℃ for 3 h to prepare a supported catalyst of ferric oxide supported on MCM-41 support.

[0011] As a preferred option, in step 1), the iron source is either ferric nitrate nonahydrate or ferric chloride hexahydrate, and more preferably ferric chloride hexahydrate. Preferably, in step 2), the calcination temperature in the muffle furnace is 500-800 ℃, and more preferably 500 ℃. Preferably, in step 3), the loading of ferric oxide is 20-65%, and more preferably 50%. To solve the second technical problem mentioned above, the present invention adopts the following technical solution: Catalyst atmosphere pretreatment: Weigh 0.2 g of 50Fe2O3 / MCM-41 catalyst into a fixed-bed quartz tube device for hydrogen production from ammonia decomposition, introduce pretreatment gas into it at a gas flow rate of 20 mL / min, and pretreat at 500℃ for 2 h at a heating rate of 5 ℃ / min.

[0012] Preferably, in step 1), the gas is hydrogen or ammonia, with ammonia being more preferred; Compared with the prior art, the present invention has at least the following beneficial effects: The catalyst prepared in this invention, using MCM-41 molecular sieve as a support to support ferric oxide, is used for ammonia decomposition to produce hydrogen. Compared with traditional ruthenium-based, cobalt-based, and iron-based catalysts, it not only reduces costs but also overcomes the obstacle of poor stability of traditional catalysts. This catalyst uses molecular sieve as a support, resulting in a catalyst with a huge specific surface area, rich and ordered mesoporous channel structure, and abundant surface properties. This confines the active species of the catalyst within the pores of the MCM-41 support and allows for the interaction between the active species and Si-OH on the MCM-41 support, thereby achieving a confinement effect and interaction between the active metal and the support, thus achieving high stability. The catalyst also employs in-situ ammonia reduction pretreatment, which enhances the catalyst's catalytic activity and saves a significant amount of equipment costs for the industrialization of ammonia decomposition compared to hydrogen reduction. Attached Figure Description

[0013] Figure 1 The diagram shows the ammonia decomposition activity of Examples 1-5. Figure 1 It can be seen that Example 1 exhibits the best activity;

[0014] Figure 2 For the TEM characterization of Example 8, from Figure 2 The ellipsoidal morphology of Example 8 can be observed;

[0015] Figure 3 The graphs show the ammonia decomposition activity of Examples 6-9 and the stability graph of Example 8. It can be seen from the graphs that 50Fe2O3 / MCM-41 has better catalytic activity, and the activity remains unchanged after 48 hours of continuous testing.

[0016] Figure 4 The figures show the catalyst activity of Examples 8 and 10. It can be seen from the figures that the catalyst for in-situ ammonia reduction in Example 8 has better ammonia decomposition activity. Detailed Implementation

[0017] The core content of this invention is illustrated below through specific examples, but it should be understood that the scope of application of this invention is not limited to these examples. Unless otherwise expressly indicated, the preparation processes and operating conditions used in the following examples follow conventional technical methods; furthermore, all reagents and materials mentioned in the examples can be obtained through conventional commercial channels unless otherwise specified.

[0018]

Example 1

[0019] Catalyst Evaluation: The ammonia decomposition performance was evaluated under ambient pressure using a continuous gas supply reaction system, maintaining the ammonia reaction gas flow rate at 20 mL / min. The ammonia feed rate was precisely controlled using a high-precision mass flow meter. Before catalytic activity testing, the catalyst was pretreated at 500 °C for 2 h using pure ammonia gas. A quartz tube reactor was used to load 200 mg of the catalyst sample to be tested. Quartz fiber cotton was used to fill and stabilize the sample inside the quartz tube to ensure the stability of the catalyst bed structure during gas-solid contact. The ammonia decomposition capacity of the catalyst sample was analyzed using a fixed-bed reactor within a temperature range of 300–600 °C.

[0020]

Example 2

[0021] Catalyst Evaluation: The ammonia decomposition performance was evaluated under ambient pressure using a continuous gas supply reaction system, maintaining the ammonia reaction gas flow rate at 20 mL / min. The ammonia feed rate was precisely controlled using a high-precision mass flow meter. Before catalytic activity testing, the catalyst was pretreated at 500 °C for 2 h using pure ammonia gas. A quartz tube reactor was used to load 200 mg of the catalyst sample to be tested. Quartz fiber cotton was used to fill and stabilize the sample inside the quartz tube to ensure the stability of the catalyst bed structure during gas-solid contact. The ammonia decomposition capacity of the catalyst sample was analyzed using a fixed-bed reactor within a temperature range of 300–600 °C.

[0022]

Example 3

[0023] Catalyst Evaluation: The ammonia decomposition performance was evaluated under ambient pressure using a continuous gas supply reaction system, maintaining the ammonia reaction gas flow rate at 20 mL / min. The ammonia feed rate was precisely controlled using a high-precision mass flow meter. Before catalytic activity testing, the catalyst was pretreated at 600 °C for 2 h using pure ammonia gas. A quartz tube reactor was used to load 200 mg of the catalyst sample to be tested. Quartz fiber cotton was used to fill and stabilize the sample inside the quartz tube to ensure the stability of the catalyst bed structure during gas-solid contact. The ammonia decomposition capacity of the catalyst sample was analyzed using a fixed-bed reactor within a temperature range of 300–600 °C.

[0024]

Example 4

[0025] Catalyst Evaluation: The ammonia decomposition performance was evaluated under ambient pressure using a continuous gas supply reaction system, maintaining the ammonia reaction gas flow rate at 20 mL / min. The ammonia feed rate was precisely controlled using a high-precision mass flow meter. Before catalytic activity testing, the catalyst was pretreated at 700 °C for 2 h using pure ammonia gas. A quartz tube reactor was used to load 200 mg of the catalyst sample to be tested. Quartz fiber cotton was used to fill and stabilize the sample inside the quartz tube to ensure the stability of the catalyst bed structure during gas-solid contact. The ammonia decomposition capacity of the catalyst sample was analyzed using a fixed-bed reactor within a temperature range of 300–600 °C.

[0026]

Example 5

[0027] Catalyst Evaluation: The ammonia decomposition performance was evaluated under ambient pressure using a continuous gas supply reaction system, maintaining the ammonia reaction gas flow rate at 20 mL / min. The ammonia feed rate was precisely controlled using a high-precision mass flow meter. Before catalytic activity testing, the catalyst was pretreated at 800 °C for 2 h using pure ammonia gas. A quartz tube reactor was used to load 200 mg of the catalyst sample to be tested. Quartz fiber cotton was used to fill and stabilize the sample inside the quartz tube to ensure the stability of the catalyst bed structure during gas-solid contact. The ammonia decomposition capacity of the catalyst sample was analyzed using a fixed-bed reactor within a temperature range of 300–600 °C.

[0028]

Example 6

[0029] Next, 70 mL of concentrated ammonia (25-28%) was mixed with 420 mL of deionized water to form an alkaline solution. Then, 2.0 g of the template agent, hexadecyltrimethylammonium bromide, was added, and the mixture was magnetically stirred for 30 min to form a homogeneous solution. Silicon-based tetraethyl orthosilicate was slowly added dropwise under continuous stirring, and the hydrolysis-condensation reaction was controlled for 2 h. The resulting white precipitate was filtered, washed, and dried in an oven at 80 ℃ for 12 h. Finally, it was calcined in a muffle furnace at 550 ℃ / min for 6 h to remove the template agent, yielding a pure silicon MCM-41 support.

[0030] Finally, 0.10 g of ferric oxide was weighed and dispersed in a crucible containing an appropriate amount of deionized water. After the dispersion was uniform, 0.4 g of MCM-41 molecular sieve was added and stirred for 30 min. Then, the crucible containing the mixed suspension was placed in an oven at 80 ℃ and dried for 12 h. Finally, it was calcined in a muffle furnace at 500 ℃ for 3 h with a heating rate of 5 ℃ / min to obtain 20Fe2O3 / MCM-41.

[0031] Catalyst Evaluation: The ammonia decomposition performance was evaluated under ambient pressure using a continuous gas supply reaction system, maintaining the ammonia reaction gas flow rate at 20 mL / min. The ammonia feed rate was precisely controlled using a high-precision mass flow meter. Before catalytic activity testing, the catalyst was pretreated at 500 °C for 2 h using pure ammonia gas. A quartz tube reactor was used to load 200 mg of the catalyst sample to be tested. Quartz fiber cotton was used to fill and stabilize the sample inside the quartz tube to ensure the stability of the catalyst bed structure during gas-solid contact. The ammonia decomposition capacity of the catalyst sample was analyzed using a fixed-bed reactor within a temperature range of 300–600 °C.

[0032]

Example 7

[0033] Next, 70 mL of concentrated ammonia (25-28%) was mixed with 420 mL of deionized water to form an alkaline solution. Then, 2.0 g of the template agent, hexadecyltrimethylammonium bromide, was added, and the mixture was magnetically stirred for 30 min to form a homogeneous solution. Silicon-based tetraethyl orthosilicate was slowly added dropwise under continuous stirring, and the hydrolysis-condensation reaction was controlled for 2 h. The resulting white precipitate was filtered, washed, and dried in an oven at 80 ℃ for 12 h. Finally, it was calcined in a muffle furnace at 550 ℃ / min for 6 h to remove the template agent, yielding a pure silicon MCM-41 support.

[0034] Finally, 0.22 g of ferric oxide was weighed and dispersed in a crucible containing an appropriate amount of deionized water. After the dispersion was uniform, 0.4 g of MCM-41 molecular sieve was added and stirred for 30 min. Then, the crucible containing the mixed suspension was placed in an oven at 80 ℃ and dried for 12 h. Finally, it was calcined in a muffle furnace at 500 ℃ for 3 h with a heating rate of 5 ℃ / min to obtain 35Fe2O3 / MCM-41.

[0035] Catalyst Evaluation: The ammonia decomposition performance was evaluated under ambient pressure using a continuous gas supply reaction system, maintaining the ammonia reaction gas flow rate at 20 mL / min. The ammonia feed rate was precisely controlled using a high-precision mass flow meter. Before catalytic activity testing, the catalyst was pretreated at 500 °C for 2 h using pure ammonia gas. A quartz tube reactor was used to load 200 mg of the catalyst sample to be tested. Quartz fiber cotton was used to fill and stabilize the sample inside the quartz tube to ensure the stability of the catalyst bed structure during gas-solid contact. The ammonia decomposition capacity of the catalyst sample was analyzed using a fixed-bed reactor within a temperature range of 300–600 °C.

[0036]

Example 8

[0037] Next, 70 mL of concentrated ammonia (25-28%) was mixed with 420 mL of deionized water to form an alkaline solution. Then, 2.0 g of the template agent, hexadecyltrimethylammonium bromide, was added, and the mixture was magnetically stirred for 30 min to form a homogeneous solution. Silicon-based tetraethyl orthosilicate was slowly added dropwise under continuous stirring, and the hydrolysis-condensation reaction was controlled for 2 h. The resulting white precipitate was filtered, washed, and dried in an oven at 80 ℃ for 12 h. Finally, it was calcined in a muffle furnace at 550 ℃ / min for 6 h to remove the template agent, yielding a pure silicon MCM-41 support.

[0038] Finally, 0.40 g of ferric oxide was weighed and dispersed in a crucible containing an appropriate amount of deionized water. After the dispersion was uniform, 0.4 g of MCM-41 molecular sieve was added and stirred for 30 min. Then, the crucible containing the mixed suspension was placed in an oven at 80 ℃ and dried for 12 h. Finally, it was calcined in a muffle furnace at 500 ℃ for 3 h with a heating rate of 5 ℃ / min to obtain 50Fe2O3 / MCM-41.

[0039] Catalyst Evaluation: The ammonia decomposition performance was evaluated under ambient pressure using a continuous gas supply reaction system, maintaining the ammonia reaction gas flow rate at 20 mL / min. The ammonia feed rate was precisely controlled using a high-precision mass flow meter. Before catalytic activity testing, the catalyst was pretreated at 500 °C for 2 h using pure ammonia gas. A quartz tube reactor was used to load 200 mg of the catalyst sample to be tested. Quartz fiber cotton was used to fill and stabilize the sample inside the quartz tube to ensure the stability of the catalyst bed structure during gas-solid contact. The ammonia decomposition capacity of the catalyst sample was analyzed using a fixed-bed reactor within a temperature range of 300–600 °C.

[0040]

Example 9

[0041] Next, 70 mL of concentrated ammonia (25-28%) was mixed with 420 mL of deionized water to form an alkaline solution. Then, 2.0 g of the template agent, hexadecyltrimethylammonium bromide, was added, and the mixture was magnetically stirred for 30 min to form a homogeneous solution. Silicon-based tetraethyl orthosilicate was slowly added dropwise under continuous stirring, and the hydrolysis-condensation reaction was controlled for 2 h. The resulting white precipitate was filtered, washed, and dried in an oven at 80 ℃ for 12 h. Finally, it was calcined in a muffle furnace at 550 ℃ / min for 6 h to remove the template agent, yielding a pure silicon MCM-41 support.

[0042] Finally, 0.74 g of ferric oxide was weighed and dispersed in a crucible containing an appropriate amount of deionized water. After the dispersion was uniform, 0.4 g of MCM-41 molecular sieve was added and stirred for 30 min. Then, the crucible containing the mixed suspension was placed in an oven at 80 ℃ and dried for 12 h. Finally, it was calcined in a muffle furnace at 500 ℃ for 3 h with a heating rate of 5 ℃ / min to obtain 65Fe2O3 / MCM-41.

[0043] Catalyst Evaluation: The ammonia decomposition performance was evaluated under ambient pressure using a continuous gas supply reaction system, maintaining the ammonia reaction gas flow rate at 20 mL / min. The ammonia feed rate was precisely controlled using a high-precision mass flow meter. Before catalytic activity testing, the catalyst was pretreated at 500 °C for 2 h using pure ammonia gas. A quartz tube reactor was used to load 200 mg of the catalyst sample to be tested. Quartz fiber cotton was used to fill and stabilize the sample inside the quartz tube to ensure the stability of the catalyst bed structure during gas-solid contact. The ammonia decomposition capacity of the catalyst sample was analyzed using a fixed-bed reactor within a temperature range of 300–600 °C.

[0044]

Example 10

[0045] Next, 70 mL of concentrated ammonia (25-28%) was mixed with 420 mL of deionized water to form an alkaline solution. Then, 2.0 g of the template agent, hexadecyltrimethylammonium bromide, was added, and the mixture was magnetically stirred for 30 min to form a homogeneous solution. Silicon-based tetraethyl orthosilicate was slowly added dropwise under continuous stirring, and the hydrolysis-condensation reaction was controlled for 2 h. The resulting white precipitate was filtered, washed, and dried in an oven at 80 ℃ for 12 h. Finally, it was calcined in a muffle furnace at 550 ℃ / min for 6 h to remove the template agent, yielding a pure silicon MCM-41 support.

[0046] Finally, 0.40 g of ferric oxide was weighed and dispersed in a crucible containing an appropriate amount of deionized water. After the dispersion was uniform, 0.4 g of MCM-41 molecular sieve was added and stirred for 30 min. Then, the crucible containing the mixed suspension was placed in an oven at 80 ℃ and dried for 12 h. Finally, it was calcined in a muffle furnace at 500 ℃ for 3 h with a heating rate of 5 ℃ / min to obtain 50Fe2O3 / MCM-41.

[0047] Catalyst Evaluation: The ammonia decomposition performance was evaluated under ambient pressure using a continuous gas supply reaction system, maintaining the ammonia reaction gas flow rate at 20 mL / min. The ammonia feed rate was precisely controlled using a high-precision mass flow meter. Before catalytic activity testing, the catalyst was pretreated at 500 °C for 2 h using pure hydrogen gas. A quartz tube reactor was used to load 200 mg of the catalyst sample to be tested. Quartz fiber cotton was used to fill and stabilize the sample inside the quartz tube to ensure the stability of the catalyst bed structure during gas-solid contact. The ammonia decomposition capacity of the catalyst sample was analyzed using a fixed-bed reactor within a temperature range of 300–600 °C.

[0048] The above description represents only some preferred embodiments of the present invention and does not constitute any limitation on the present invention. Any simple adjustments, variations, or equivalent substitutions made to the above embodiments based on the core principles of the present invention are considered to fall within the protection scope covered by the technical solutions of the present invention.

Claims

1. A highly efficient iron-based ammonia decomposition catalyst based on MCM-41 support, its preparation method and application, characterized in that... Supported catalysts of ferric oxide supported on mesoporous MCM-41 molecular sieve.

2. The method for preparing the catalyst according to claim 1, comprising the following steps: Preparation of ferric oxide: First, 1.6 g of iron source and 6.3 g of sodium acetate were weighed and added to 60 mL of ethanol, and the solution was stirred at room temperature for 30 min. Next, 1 mL of deionized water was added to the prepared solution, and the mixture was stirred for 30 min. Then, the solution was transferred to a 100 mL hydrothermal reactor and kept at 180 °C for 24 h. Finally, the mixture was filtered, washed three times each with deionized water and ethanol, and placed in an 80 °C oven until completely dry. After drying, the sample was placed in a muffle furnace and calcined at a certain temperature with a heating rate of 5 °C / min. Preparation of MCM-41 molecular sieve: Weigh 2.0 g of cetyltrimethylammonium bromide and dissolve 70 mL of concentrated ammonia in 420 mL of water. After the solution is clear, add 10 mL of tetraethyl orthosilicate and stir for 2 h. Filter the solution and wash it three times each with deionized water and ethanol. Dry it completely in an oven at 80 ℃. After drying, place the sample in a muffle furnace and calcine it at 550 ℃ for 5 h at a heating rate of 5 ℃ / min. Preparation of supported catalyst: A certain amount of ferric oxide was weighed and dispersed in a crucible containing an appropriate amount of deionized water. After the dispersion was uniform, 0.4 g of support was added and stirred for 30 min. Then, the crucible containing the mixed suspension was placed in an oven at 80 ℃ and dried for 12 h. Finally, it was calcined in a muffle furnace at a heating rate of 5 ℃ / min to 500 ℃ for 3 h to prepare a supported catalyst of ferric oxide supported on MCM-41 support. Catalyst activity evaluation: The ammonia decomposition performance was assessed under ambient pressure using a continuous gas supply reaction system, maintaining the ammonia reaction gas flow rate at 20 mL / min. The ammonia feed rate was precisely controlled using a high-precision mass flow meter. Before catalytic activity testing, the catalyst was kept at a specific temperature under pretreated gas for 2 hours. A quartz tube reactor was used to load 200 mg of the catalyst sample to be tested. Quartz fiber cotton was used to fill and stabilize the sample inside the quartz tube to ensure the stability of the catalyst bed structure during gas-solid contact. The ammonia decomposition capacity of the catalyst sample was analyzed using a fixed-bed reactor within a temperature range of 300–600 °C.

3. The preparation method according to claim 2, characterized in that: The iron source is either ferric nitrate nonahydrate or ferric chloride hexahydrate, and the calcination temperature is one of 500, 600, 700, or 800 ℃. A certain amount of ferric oxide is one of 0.10, 0.22, 0.40, or 0.

74.

4. The application of the supported catalyst prepared according to any one of the catalysts described in claims 1 and 2 in the ammonia decomposition for hydrogen production.

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